Immediately after the events of The Desolation of Smaug, Bilbo and the dwarves try to defend Erebor's mountain of treasure from others who claim it: the men of the ruined Laketown and the elves of Mirkwood.

The ultimate X-Men ensemble fights a war for the survival of the species across two time periods as they join forces with their younger selves in an epic battle that must change the past – to save our future.